Electrochemical cells

ABSTRACT

An electrochemical cell includes a hydrogen generator and a hydrogen fuel cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Ser. No. 10/438,318, filed onMay 15, 2003, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates to electrochemical cells.

BACKGROUND

An electrochemical cell is a device capable of providing electricalenergy from an electrochemical reaction, typically between two or morereactants. Generally, an electrochemical cell includes two electrodes,called an anode and a cathode, and an electrolyte disposed between theelectrodes. In order to prevent direct reaction of the active materialof the anode and the active material of the cathode, the electrodes areelectrically isolated from each other by a separator.

In one type of electrochemical cell, sometimes called a hydrogen fuelcell, the anode reactant is hydrogen gas, and the cathode reactant isoxygen (e.g., from air). At the anode, oxidation of hydrogen producesprotons and electrons. The protons flow from the anode, through theelectrolyte, and to the cathode. The electrons flow from the anode tothe cathode through an external electrical conductor, which can provideelectrical energy. At the cathode, the protons and the electrons reactwith oxygen to form water.

In another type of electrochemical cell, called a metal-air cell, oxygenis reduced at the cathode, and a metal (e.g., zinc) is oxidized at theanode. Electrons flow from the anode to the cathode through an externalelectrical conductor, which can provide electrical energy. Oxygen can besupplied to the cathode from the atmospheric air external to the cellthrough one or more air hole(s) in the cell housing. An electrolyticsolution (e.g., an alkaline electrolyte, such as a potassium hydroxidesolution) in contact with the electrodes contains ions that flow throughthe separator between the electrodes to maintain charge balancethroughout the cell during discharge.

Metal-air cells can experience carbonation, in which the alkalineelectrolyte in the cathode absorbs carbon dioxide, resulting in theprecipitation of carbonate salts (such as potassium carbonate or sodiumcarbonate). These salts can have a detrimental effect on the cell by,for example, blocking cathode pores or air access holes on the cathodeside of the cell envelope. A result can be that the cathode has lessaccess to the oxygen it needs to finction.

Furthermore, a metal-air cell can experience water exchange with itsenvironment, as a result of the difference in the relative humidity ofthe environment and the equilibrium vapor pressure of the cellelectrolyte. When the ambient air is drier (i.e., has a lower partialpressure of water vapor) than the electrolyte, the cell can lose waterto the environment and dry out. On the other hand, when the ambient airis wetter (i.e., has a higher partial pressure of water vapor) than theelectrolyte, the cell can gain water, such that the cathode ultimatelyfloods with electrolyte solution. In either case, a consequence is thatthe cell can lose its ability to support heavy currents. Additionally,when the cathode is flooded with electrolyte solution, the electrolytesolution can eventually leak out of the air access holes.

SUMMARY

In general, an electrochemical cell includes an electrochemical hydrogengenerator connected to a hydrogen fuel cell. The hydrogen generator andthe fuel cell can be electrically and/or mechanically connected.

In one aspect, an electrochemical cell includes an electrochemicalhydrogen generator and a hydrogen fuel cell. The electrochemicalhydrogen generator has a first cathode which generates hydrogen gas, anda first anode which is adjacent to the first cathode. The hydrogen fuelcell includes a second anode which oxidizes hydrogen gas, and a secondcathode which is adjacent to the second anode. The first anode iselectrically connected to the second cathode, and the first cathode iselectrically connected to the second anode.

In another aspect, an electrochemical cell includes an electrochemicalhydrogen generator in series electrical connection with a hydrogen fuelcell.

In some embodiments, the electrochemical hydrogen generator includes afirst cathode which generates hydrogen gas and a first anode which isadjacent to the first cathode. The hydrogen fuel cell can include asecond anode which oxidizes hydrogen gas and a second cathode which isadjacent to the second anode. In some cases, the first anode iselectrically connected to the second cathode and the first cathode iselectrically connected to the second anode.

In some embodiments, the hydrogen fuel cell includes a second anodewhich oxidizes hydrogen gas and a second cathode which is adjacent tothe second anode.

In some cases, the hydrogen generator includes a gas outlet, and thehydrogen fuel cell includes a gas inlet in fluid communication with thegas outlet. The hydrogen generator can have a first housing. Thehydrogen fuel cell can include a second housing. In some embodiments,the first housing is releasably engageable with the second housing. Insome cases, the hydrogen fuel cell and the hydrogen generator aredisposed within a single housing.

The hydrogen generator can include a hydrogen-generating anode. Thehydrogen-generating anode can be a metal (e.g., zinc, aluminum,titanium, zirconium, and tin). The hydrogen-generating anode can includea hydrogen storage composition (e.g., a metal hydride or a misch metalalloy).

In some cases, the hydrogen fuel cell has an acidic polymer membraneelectrolyte.

In some embodiments, the electrochemical cell further includes acontroller. The electrochemical cell can further include a sensor. Thesensor can be connected to the controller.

In another aspect, an electrochemical cell includes an electrochemicalhydrogen generator and a hydrogen fuel cell. The hydrogen generator hasa first cathode which generates hydrogen gas, and a first anode which isopposed to the first cathode. The hydrogen fuel cell has a second anodewhich oxidizes hydrogen gas, and a second cathode which is opposed tothe second anode. There is a coupling between the hydrogen generator andthe hydrogen fuel cell. The coupling fluidly connects the first cathodeto the second anode.

In some embodiments, the hydrogen generator further includes a firsthousing within which the first anode and the first cathode are disposed.In some cases, the hydrogen fuel cell further includes a second housingwithin which the second anode and the second cathode are disposed. Thesecond housing can be releasably engageable with the first housing.

The first anode can be electrically connected to the second cathode.

In another aspect, a method of generating an electrical current includesforming an electrical connection between a first anode of anelectrochemical hydrogen generator and a second cathode of a hydrogenfuel cell, and forming an electrical connection between a first cathodeof the electrochemical hydrogen generator and a second anode of thehydrogen fuel cell.

In some cases, the first cathode generates hydrogen gas, and the firstanode is adjacent to the first cathode. The second anode can oxidizehydrogen gas, and the second cathode can be adjacent to the secondanode.

In another aspect, a method of generating an electrical current includesgenerating a first electron from an oxidation half cell of anelectrochemical hydrogen generator, and transmitting the first electronto a reduction half cell of a hydrogen fuel cell.

In some embodiments, the method further includes transmitting a secondelectron from an oxidation half cell of the hydrogen fuel cell to areduction half cell of the hydrogen generator. The method can furtherinclude generating hydrogen from the hydrogen generator and oxidizingthe generated hydrogen at the fuel cell. In some cases, the methodfurther includes transmitting the generated hydrogen to the fuel cellthrough a conduit fluidly-connecting the hydrogen generator and the fuelcell.

In another aspect, an electrochemical hydrogen generator includes ahousing with a hydrogen outlet, an anode in the housing including anoxidizable material, a cathode in the housing including a hydrogengeneration catalyst, and an ionically conductive, electricallyinsulative separator layer between the anode and the cathode.

In some cases, the hydrogen generator further includes an aqueous ionicelectrolyte within the housing.

The oxidizable material can include a metal (e.g., a Group IIa metal, aGroup Ib metal, a Group IIIa metal, a Group IIb metal, iron, tin,manganese, titanium, zirconium, or a combination thereof).

The separator can include a non-woven fibrous polymer fabric (e.g.,polyvinyl alcohol fibers). In some cases, the non-woven fibrous polymerfabric is laminated to cellophane.

In some embodiments, the cathode further includes a binder (e.g., highdensity polyethylene or polytetrafluoroethylene) containing thecatalyst.

The hydrogen outlet can include a hydrophobic membrane arranged toprevent leakage of a liquid from the housing.

The oxidizable material can include a metal hydride (e.g., titaniumhydride, zirconium hydride, a reversible hydride of nickel or lanthanum,or a misch metal alloy). In some cases, the oxidizable material includesa metal (e.g., zinc, aluminum, titanium, zirconium, or tin).

The hydrogen generator can further include an alkaline electrolyte(e.g., aqueous sodium hydroxide or aqueous potassium hydroxide) disposedin the housing.

The anode and the cathode can be connected by an electronic conductor,and the electronic conductor can include a switch.

Embodiments of a hydrogen generator can include one or more of thefollowing advantages. The hydrogen generator can have competitivevolumetric and gravimetric capacities relative to other hydrogensources. In some cases, the hydrogen generator can be safer thanhydrogen sources based on liquid hydrogen, compressed hydrogen gas,metal hydride storage alloys, or active metal hydrides. The hydrogengenerator can experience reduced leakage of hydrogen gas and/orelectrolyte compared to other hydrogen sources.

In embodiments in which the anode layer of the hydrogen generator isexposed to cathode material on two of its sides, the hydrogen generatorcan produce more hydrogen gas than a comparable hydrogen generatorwithout such a structure. The hydrogen generator can be activated ordeactivated in accordance with hydrogen gas demand, which can beregulated by closing an electrical circuit on the generator. When thehydrogen generator is deactivated, the generator does not exhibit asubstantial internal pressure of hydrogen. The components of thehydrogen generator can be relatively inexpensive, compared to thecomponents of other hydrogen sources.

The hydrogen generator can provide fuel to a fuel cell safely andreliably, and in a controllable manner. The hydrogen generator can be aneconomical, compact, portable, and/or disposable source of hydrogen gas.The hydrogen generator can be of a low weight relative to hydrogensources employing reversible metal hydride alloys. The materials used inthe hydrogen generator can be environmentally benign or can have minimalenvironmental impact. For example, a used hydrogen generator can haveproducts substantially similar to those of a used alkaline battery.Thus, the hydrogen generator can be easily discarded, without thenecessity of taking extra precautions. The hydrogen generator canwithstand exposure to moderately high temperatures (e.g., 71° C.)without generating excessive quantities of unwanted hydrogen gas ordangerous internal pressures. The hydrogen generator can have a shelflife of at least ten years, such that it can be stored prior to initialuse and between uses, without losing its ability to be activated orreactivated.

Embodiments of an electrochemical cell including a fuel cell and ahydrogen generator can include one or more of the following advantages.The electrochemical cell can experience reduced carbonation, drying,and/or flooding relative to a conventional metal-air cell. Theelectrochemical cell can therefore have an improved activated stand liferelative to a conventional metal-air cell. In embodiments in which theelectrochemical cell includes a water-recycling feature, the cell can besmaller and lighter, and can have an increased volumetric capacity forhydrogen gas, relative to a cell without the water-recycling feature.The electrochemical cell can produce a higher voltage than aconventional fuel cell.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features andadvantages of the invention will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1 and 1A are partial cross-sectional side views ofhydrogen-generating cells.

FIG. 2 is a cross-sectional side view of an electrochemical cell.

FIG. 3 is a schematic of an electrochemical cell.

DETAILED DESCRIPTION

Referring to FIG. 1, a hydrogen generator 10 includes a housing 12defining an internal volume 14. Within the internal volume of thehydrogen generator is a cathode 16 which contains a cathode catalystmaterial. Cathode 16 forms a layer 15 at the center of housing 12 and alayer 17 near the outer perimeter of the housing. Housing 12 furtherincludes a separator 18 that forms an envelope 20. The envelope ispositioned between the center cathode layer 15 and the perimeter cathodelayer 17. Envelope 20 encases an anode 22 which contains anode activematerial. Cathode 16 and anode 22 both are submerged in a commonelectrolyte.

In the hydrogen generator 10 of FIG. 1, cathode 16 is separated fromanode 22; i.e., the cathode is located on a metal substrate which isseparate from, and not permanently connected to, the anode.

Anode 22 can be formed of any of the standard materials used in analkaline battery anode. For example, anode 22 can be a gel that includesmetal (e.g., metal particles), a gelling agent, and minor amounts ofadditives, such as gassing inhibitor.

A suitable anode metal includes a Group IIa metal, a Group Ib metal, aGroup IIIa metal, a Group IIb metal, iron, tin, manganese, titanium orzirconium. For example, the anode metal can include zinc.

The anode metal can be zinc in the form of particles, such as those thatare conventionally used in zinc slurry anodes. The anode can include,for example, between 60% by weight and 80% by weight, between 65% byweight and 75% by weight, or between 67% by weight and 71% by weight ofzinc particles. The zinc particles can be small zinc-based particles,such as zinc fines or zinc dust. A zinc-based particle can be formed ofzinc or a zinc alloy. A zinc-based particle can be formed bymanufacturing processes including gas atomization, centrifugalatomization, melt spinning, and air blowing.

Zinc fines are zinc-based particles that have dimensions suitable topass through a standard 200 mesh screen (i.e., −200 mesh) in a normalsieving operation, such as when a sieve is shaken by hand. Zinc dustcontains zinc-based particles that have dimensions suitable to passthrough a standard 325 mesh screen (i.e., −325 mesh) in a normal sievingoperation. The zinc-based particles can be nominally spherical ornonspherical in shape. Nonspherical particles can be acicular in shape(i.e., having a length along a major axis at least two times a lengthalong a minor axis) or flake-like in shape (i.e., having a thickness nomore than 20 percent of the maximum linear dimension). The zincparticles can have a surface area of between 200 cm²/gram and 300cm²/gram.

In some embodiments, the anode can include a hydrogen storagecomposition, such as a metal hydride (e.g., titanium hydride, zirconiumhydride, reversible hydrides of nickel or lanthanum, or a misch metal).

Anode 22 can include a gelling agent. Examples of gelling agents includepolyacrylic acids, grafted starch materials, salts of polyacrylic acids,polyacrylates, carboxymethylcellulose, or combinations thereof. Examplesof such polyacrylic acids are Carbopol 940 and 934 (available from B. F.Goodrich) and Polygel 4P (available from 3V), and an example of agrafted starch material is Waterlock A211 (available from GrainProcessing Corporation, Muscatine, Iowa). An example of a salt of apolyacrylic acid is Alcosorb G1 (available from Ciba Specialties).

Anode 22 preferably has a high surface area in order to support a rapidrate of dissolution of the anode active material and electronproduction, as well as a high rate of hydrogen gas generation on thecatalyst cathode. For example, anode 22 can have a surface area between50 cm²/gram and 500 cm²/gram.

Cathode 16 can include a noble metal catalyst, for example, palladiumand/or ruthenium catalytic material. The cathode catalytic materials canbe supported on carbon and coated on a fine metal gauze or mesh, such asnickel EXMET™, available from Exmet Corp. (Naugatuck, Conn.). Forexample, a suitable cathode includes carbon-supported palladium andcarbon-supported ruthenium coated (e.g., painted) on a nickel EXMET™.The cathode coating can include between 0.5% by weight and 2% by weightof 1% palladium supported on activated carbon, available from AlfaAesar, and between 2% by weight and 6% by weight of 5% rutheniumsupported on activated carbon, available from Alfa Aesar.

The cathode coating can include a binder. Examples of binders includepolyethylene powders, polypropylene, polybutylene, nylon,polyacrylamides, acrylics, polyvinyl chloride, polystyrene,polymethylpentene, Portland cement, and fluorocarbon resins, such aspolyvinylidene fluoride and polytetrafluoroethylene. An example of apolyethylene binder is powdered high-density polyethylene (e.g.,Coathylene HA-1681, available from Hoechst). The cathode coating caninclude between 0.1% and 1% binder by weight.

In some cases, the cathode includes a carbon-supported palladium andruthenium catalyst and a binder that is less hydrophobic thanpolytetrafluoroethylene (such as powdered high density polyethylene)coated on a nickel EXMET™ screen.

For example, a catalyst cathode coating including 14% powdered highdensity polyethylene (Coathylene Grade HA-1681, from Hoechst-CelaneseCorp.), 50% n-propanol, 1% of 1% palladium on activated carbon (fromAlfa Aesar), 4% of 5% ruthenium on activated carbon (from Alfa Aesar),and 31% activated carbon powder (from Alfa Aesar) was prepared asfollows. The powdered high density polyethylene and the n-propanol weremixed. Thereafter, the carbon-supported palladium and thecarbon-supported ruthenium were added to the mixture, creating a slurry.(In some cases, the carbon supported catalyst material can be added tothe mixture as a water suspension (e.g., 50% solids and 50% water). Insuch cases, the weight of water, which will be evaporated in subsequentsteps, is not counted in the recipe.) The slurry was then coated onto anickel EXMET™ screen by brushing or coating using a doctor blade. Afterthe liquid evaporated, the coated screen was heated in an oven at 190°C. for ten minutes, to sinter the binder and powdered catalystcomponents to the screen.

Cathode 16 can include other additives. For example, the cathode caninclude a surfactant (e.g., Triton X-100, available from Sigma-Aldrich).The surfactant can help to wet the cathode, thereby preventing thebinder from coagulating and decreasing the effectiveness of the cathodematerial.

Electrolyte 24 can be an alkaline electrolyte (e.g., potassium hydroxideor sodium hydroxide). In some cases, the electrolyte contains dissolvedsalts, oxides, or hydroxides of bismuth, tin, indium, mercury, lead,cadmium, or thallium. The electrolyte can include a dissolved cation oranion of the metal anode (e.g., an aluminum oxide, sodium aluminate,potassium aluminate, a zinc oxide, a zinc hydroxide, or calcium salts).In some embodiments, the electrolyte contains corrosion inhibitors, suchas quaternary ammonium salts or a non-ionic, anionic, or cationicsurfactant.

Envelope 20 also encases a current collector 26. The current collectorcoils through the anode active material. An electronic conductor 28 isconnected to current collector 26 and terminates outside of the cell.Another electronic conductor 30 is connected to cathode 16 and alsoterminates outside of the cell. Conductor 28 is insulated by, forexample, a plastic coating, as the conductor passes through the interiorvolume of the housing, before it exits the housing.

When conductors 28 and 30 make contact, current begins to flow throughthem. When current begins to flow through them, zinc is oxidized at theanode and water is reduced at the cathode, leading to an overallreaction in which hydrogen gas is produced according to equations (1),(2) and (3):Zn+2OH⁻→ZnO+H₂O+2e ⁻  (1)2H₂O+2e ⁻→2OH⁻+H₂   (2)Zn+H₂O→ZnO+H₂   (3)Housing 12 includes a hydrogen gas outlet 34, through which hydrogen gascan exit the housing.

Other embodiments of a hydrogen generator are possible. Referring toFIG. 1A, a hydrogen generator 210 has a reverse configuration of thehydrogen generator 10 of FIG. 1. Hydrogen generator 210 includes ahousing 212 defining an internal volume 214. Anode 216 forms a layer 218at the center of the housing and a layer 220 near the outer perimeter ofthe housing. Anode layers 218 and 220 further include current collectors221 and 223. Current collectors 221 and 223 are connected to each other,either within the housing or exterior to the housing. A separator 222forms an envelope 224 which encases cathode 226. The envelope ispositioned between the center anode layer 218 and the perimeter anodelayer 220. An electronic conductor 228 is connected to currentcollectors 221 and 223, and extends outside of the cell. Anotherelectronic conductor 230 is connected to cathode 226, and also extendsoutside of the cell. When conductors 228 and 230 make contact, currentbegins to flow through them.

Separator 18 can be a laminate of a non-woven fabric and a membrane(e.g., DURALAM™, from the Gillette Company). The non-woven layer can bea fibrous polymer fabric (e.g., polyvinyl alcohol fibers). The separatorcan include a single layer or multiple layers of the non-woven fabric.The non-woven fibrous polymer fabric can be laminated to a membrane suchas cellophane. In some cases, the separator is pleated, and thus canallow for the expansion of zinc when it reacts to form zinc oxide. Withsuch a configuration, the separator can expand without tearing.

Housing 12 can be a cylindrical housing. The housing can have a lengthof between 2.5 cm and 30 cm, and a width or diameter of between 1 cm and20 cm. The housing can have a volume of between 2 cm³ and 9,400 cm³. Thehydrogen generator can have a mass of between 2.5 grams and 25kilograms.

Housing 12 can be, for example, a plastic or a metal. Suitable metalsinclude brass, copper, tin, steel, stainless steel, nickel, orcombinations thereof. The housing can include an inner metal wall and anouter electrically non-conductive material, such as heat-shrinkableplastic. When the housing is metal, it can serve as a current collectoror as an electrical feedthrough from a current collector to the exteriorof the generator.

In the hydrogen generator 10 of FIG. 1, in which the cathode approachesor contacts the housing, preferred materials for the housing includesteel, stainless steel, nickel, or combinations thereof. The housing mayalso be coated or plated on its interior surface with nickel, cobalt,tin, or a carbon conductive coating, in order to lower the electricalresistance of the interface between the housing and the cathode.

In the hydrogen generator 210 of FIG. 1A, in which the anode approachesor contacts the housing, the preferred materials for the housing arecopper, brass, tin, or combinations thereof. The housing may also becoated or plated on its interior surface with bismuth, tin, indium,cadmium, lead, or thallium, in order to minimize hydrogen gas evolutiondirectly from the anode when the generator is deactivated.

Hydrogen gas outlet 34 in housing 12 can be equipped with a hydrophobic,hydrogen-permeable membrane 36 (e.g., a fluoropolymer membrane.)Suitable membranes are available from Pall Corp. (East Hills, N.Y.), orW. L. Gore and Associates, Inc. (Dallas, Tex.). The membrane can help tolimit or prevent electrolyte leakage from the housing. Although housing12 in FIG. 1 has only one hydrogen gas outlet, in some cases the housinghas more than one hydrogen gas outlet (e.g., between 2 and 8 hydrogengas outlets).

To decrease the rate of gassing when the hydrogen generator is turnedoff (i.e., when conductors 28 and 30 are not in contact with eachother), the anode metal can be an alloy with gassing inhibitors, such asbismuth, tin, indium, mercury, lead, cadmium, or thallium. Preferredalloying elements include bismuth, tin, and indium. For example, themetal can be a zinc alloy including up to 500 ppm indium and up to 500ppm bismuth. Traces of other metals (e.g., aluminum or calcium) may alsobe added in order to suppress localized hydrogen gas evolution at themetal anode, or to promote beneficial action of any tin, indium, orbismuth that is alloyed with the anode metal.

Electronic conductors 28, 30, 228, and 230 can include copper or brasswire. The wire can be plated or coated with a thin layer of indium, tin,or lead. Because the anodic and cathodic reactions are localized on twoseparate electrodes having separator material between them, theelectrochemical reaction between the electrodes may not occur until theelectronic conductors make contact with each other. When the conductorsmake contact, the electrochemical reaction can begin, resulting in theproduction of hydrogen gas. In some cases, the conductors are insulatedby, e.g., a sheath of perfluoroalkoxy TEFLON™ (available from DuPont),to prevent the conductors from making undesirable contact with othermaterials within the housing. Conductor 28 can be soldered, welded, ormechanically fixed to current collector 26, and conductor 228 can besoldered, welded, or mechanically fixed to current collectors 221 and223. Conductor 30 can be soldered, welded, or mechanically fixed to thecathode screen of cathode 16, and conductor 230 can be soldered, welded,or mechanically fixed to the cathode screen of cathode 226. In order tolimit or prevent corrosion, the joints can be covered in, e.g., asphalt.

An example of a hydrogen generator was prepared as follows.

A polypropylene container (about 2.75 centimeters in diameter and about4.75 centimeters in length) was perforated by drilling approximately 120holes, each about 3 millimeters in diameter, in a regular distributionover the container surface.

The container was wrapped with a DURALAM™ battery separator (from theGillette Company) on its outside surface. The overlapping seams and endsof the separator were sealed using a solution of asphalt in toluene.

A cathode was placed within the container. The cathode included a wovennickel screen (3.75 centimeters×10.75 centimeters) pasted with a 50/50mixture of 1% palladium supported on carbon black, 5% rutheniumsupported on carbon black, and a fluoropolymer (TEFLON™ Dupont producttype 30, available from DuPont). Approximately 3.34 grams of catalyzedcarbon black were included for every 1.17 milliliters of Teflonemulsion. The total weight of the dry coating was 2.34 grams (on 40.3cm² of nickel screen). The catalyzed cathode included 11.7 milligrams ofpalladium and 58.5 milligrams of ruthenium.

The catalyst screen was soldered to a polyurethane foam-sheathed copperwire. The wire was threaded through an asphalt-sealed feedthrough to theexterior of the outer container. The solder joint to the nickel screenwas covered in asphalt.

The assembly was disposed co-axially within a second container. Thesecond container was a polyethylene tube that was approximately 3.25centimeters in diameter and ten centimeters in length.

The second container was disposed coaxially within a third container.The third container was a heavy-walled fluoropolymer pipe with screwedendcaps.

The innermost container was filled with 9N potassium hydroxide solution.

The innermost container communicated through both of its ends to thethird, outer, container, which was partially filled with more 9Npotassium hydroxide.

The annular space between the separator (wrapped around the perforatedinner container) and the second, middle, container was filled with agelled, alkaline, zinc powder slurry containing 64% zinc. Within thisannular compartment there was also a spiral copper wire which contactedthe zinc slurry. The wire was threaded through an asphalt-sealedfeedthrough in the outer container to the exterior of the apparatus.

The hydrogen generator 10 of FIG. 1 can be used as a hydrogen sourcefor, e.g., a hydrogen fuel cell, in an electrochemical cell similar tothat described below with reference to FIG. 2.

Referring to FIG. 2, an electrochemical cell 110 has a housing 111.Within housing 111 is a hydrogen generator 112 that is connected to ahydrogen fuel cell 114. The hydrogen generator includes a housing 116defining an internal volume 118. Disposed within the internal volume arean anode 120 and a cathode 122, separated by a separator 124. Thehydrogen generator also includes a conductor 126 having a switch 128. Anelectrolyte permeates most of the void space in the hydrogen generator,filling the pores in separator 124 and contacting both anode 120 andcathode 122.

The fuel cell 114 has a housing 130 defining an internal volume 132.Within the internal volume are an anode 134 and a cathode 136, separatedby an electrolyte 138. The housing also has an oxygen or air inlet 140,a water outlet 142 (through which oxygen-depleted air can also escape),and a hydrogen inlet 144. The hydrogen inlet 144 is releasablyconnected, by means of a connector 146, to a hydrogen gas outlet 148 inhydrogen generator housing 116. The connection between the hydrogengenerator and the hydrogen fuel cell can provide a conduit for hydrogengas. Thus, hydrogen gas produced by the hydrogen generator can travel tothe fuel cell, where it can be consumed by fuel cell anode 134. Theconnection between the hydrogen generator and the fuel cell can beclosed or opened as needed.

The hydrogen generator can include a gas-permeable, liquid-impermeablemembrane 145, such as Gore, EXCELLERATOR™ Gas Diffusion Membrane (4 mil,part number 243042966, available from W. L. Gore Associates, Dallas,Tex.), to limit or prevent undesirable leakage into or out of thegenerator. For the same reason, the fuel cell can include a similargas-permeable, liquid-impermeable membrane 149.

FIG. 2 shows the electrochemical cell 110, the fuel cell 114, and thehydrogen generator 112 each with their own housings. In some cases,however, the fuel cell and the hydrogen generator both are disposedwithin a single housing, with an integral coupling between the fuel celland the generator to transmit hydrogen gas. The fuel cell and thehydrogen generator can be in individual, attachable housings that arenot located in one big housing. In some cases, the hydrogen generatorcan be detached from the fuel cell, disposed of, and replaced with a newhydrogen generator.

In addition to being connected mechanically, the hydrogen generator andhydrogen fuel cell can also be in electrical connection with each other,as shown in FIG. 2. In FIG. 2, a conductor 150 connects hydrogengenerator anode 120 to fuel cell cathode 136. Conductor 150 can includea load 152. A second conductor 154 connects hydrogen generator cathode122 to fuel cell anode 134. Conductor 154 can have a switch 156. Whenswitch 156 is activated, the fuel cell and the hydrogen generator are inseries electrical connection.

When the hydrogen generator and the hydrogen fuel cell are electricallyconnected to each other in this way, the voltage produced by thehydrogen generator (e.g., up to 0.4 V) is added to that produced by thefuel cell (e.g., around 1.0V), to produce a final voltage of, e.g., upto 1.4 V.

In some cases, the hydrogen generator is not electrically connected tothe fuel cell. In such cases, a switch 128 (shown in FIG. 2) establishesan electrical connection between anode 120 and cathode 122 of thehydrogen generator. When switch 128 is closed, the hydrogen generatorproduces hydrogen. In such a case, it is preferable for theelectrochemical cell to include a control or controls which sensehydrogen flow or pressure, and which can automatically control theaction of switch 128. The rate of hydrogen generation can be controlledto balance it with the rate of hydrogen consumption by the fuel cell sothat a moderate constant flow and pressure is maintained, in balancewith the demand of the fuel cell.

During operation of electrochemical cell 110 of FIG. 2 in the serieselectrical connection mode, hydrogen leakage can occur between thegenerator and the fuel cell sections. As a result, the hydrogen pressureat fuel cell inlet 144 can decline. In such cases, switch 128 can betemporarily closed whenever the pressure drops below a certain minimumthreshold. Such an action can occur automatically, in response to asignal from, for example, a pressure gauge or transducer whichcommunicates either to hydrogen outlet 148 of the generator or tohydrogen inlet 144 of the fuel cell. Alternatively, a form ofproportional control may be applied to regulate the current at switch128, thereby maintaining a smooth, constant regulation of hydrogenpressure. When proportional control is used, the switch 128 is notsimply an on-off switch. Rather, it regulates hydrogen generation inproportion to the degree to which the actual pressure deviates from adesired operating pressure. If the actual pressure is only slightlybelow the desired pressure, then a small current is allowed to flowthrough switch 128. If the actual pressure is substantially below thedesired pressure, then a large current is allowed to flow through switch128.

The hydrogen generator in electrochemical cell 110 of FIG. 2 can be, forexample, the hydrogen generator 10 described with reference to FIG. 1.When conductors 28 and 30 make contact, the reactions of equations (1),(2), and (3) take place in the hydrogen generator.

The hydrogen gas that is produced by the hydrogen generator in itsoverall reaction travels through hydrogen outlet 148 and into hydrogeninlet 144, where it can be used by the fuel cell 114 to generatecurrent. The electrons produced at anode 120 move through conductor 150to fuel cell cathode 136, where the electrons can be used in thereduction reaction that occurs at that site.

In fuel cell 114, anode 134 oxidizes hydrogen gas to produce protons andelectrons. The protons move through electrolyte 138 to cathode 136,where the protons combine with oxygen, provided through oxygen or airinlet 140, and electrons traveling through conductor 150 to producewater. The water can exit the fuel cell through water outlet 142. Theelectrons produced by the oxidation move through conductor 154 (ifswitch 156 is closed), to hydrogen generator cathode 122, where they canbe used to reduce water.

Referring to FIG. 3, in some cases water that exits through water outlet142 of hydrogen fuel cell 114 can be recycled to hydrogen generator 112by, for example, a pump 115. At hydrogen generator 112, the water can bereduced to form more hydrogen gas.

Thus, in the fuel cell, water is produced in an overall reactionaccording to equations (4), (5), and (6):H₂→2H⁺+2e ⁻  (4)½O₂+2H⁺+2e ⁻→H₂O   (5)H₂+½O²→H₂O   (6)

The overall reaction for electrochemical cell 110, therefore, is that ofequation (7):Zn+½O₂→ZnO   (7)

The anode 134 of the fuel cell can be formed of a material capable ofinteracting with hydrogen gas to form protons and electrons. Thematerial can be any material capable of catalyzing the dissociation andoxidation of hydrogen gas. Examples of such materials include, forexample, platinum, platinum alloys, such as platinum-ruthenium, andplatinum dispersed on carbon black.

Cathode 136 can be formed of a material capable of catalyzing thereaction between oxygen, electrons, and protons to form water. Examplesof such materials include, for example, platinum, platinum alloys,transition metals, transition metal oxides, and noble metals dispersedon carbon black.

Electrolyte 138 is capable of allowing ions to flow through it whilealso providing a substantial resistance to the flow of electrons. Insome embodiments, electrolyte 138 is a solid polymer (e.g., a solidpolymer ion exchange membrane). Electrolyte 138 can be a solid polymerproton exchange membrane. An example of a solid polymer proton exchangemembrane is a solid polymer containing sulfonic acid groups. Suchmembranes are commercially available from E.I. DuPont de Nemours Company(Wilmington, Del.) under the trademark NAFION. Alternatively,electrolyte 138 can also be prepared from the commercial productGORE-SELECT, available from W.L. Gore & Associates (Elkton, Md.). Insome cases, electrolyte 138 can be a polyphosphazine membrane or a bulkacid (such as phosphoric acid).

In some embodiments, electrolyte 138 can be an ionically conductingliquid electrolyte (e.g., aqueous potassium hydroxide solution, aqueoussodium hydroxide solution, aqueous sulfiric acid solution, or aqueousphosphoric acid solution). The liquid electrolyte can be a free liquidor it can be immobilized by the addition of a gelling agent, such as apolymer (e.g., polyacrylic acid or polymethacrylic acid), or anabsorbing agent (e.g., silica gel, fumed silica, or clay).

Housing 130 can be any conventional housing commonly used in fuel cells.For example, housing 130 can be a plastic, carbon, or metal containersuch as steel, stainless steel, graphite, nylon, polyvinyl chloride,poly-tetrafluoroethylene, polyvinylidene fluoride, perfluoro-alkoxyresin, or a combination of metals, carbons, and plastics. Plastics maybe filled, e.g., with mineral fillers. Alternatively, plastics may beunfilled.

Hydrogen generator 112 can be primed so that hydrogen gas is immediatelyavailable to fuel cell 114 when switch 156 is closed and electrochemicalcell 110 is activated. When switch 128 on the hydrogen generator isclosed, the hydrogen generator starts to generate hydrogen. If connector146 is closed, then hydrogen gas can build up in hydrogen outlet 148.Once connector 146 is opened, the hydrogen gas will be immediatelyavailable to fuel cell 114.

Referring to FIG. 3, in some cases electrochemical cell 110 includes asensor 310, which sends an electrical signal to a controller 312.Controller 312 then activates or deactivates hydrogen generator 112according to the signal. The controller and the sensor can be connectedto each other by an electronic signal conditioning device (e.g., anelectronic filter that can fix spikes or dips in the sensor signal, suchas those caused by vibration or shock). The controller can be connectedto a conductor. In response to a signal from, e.g., the sensor, thecontroller can cause a variable amount of current to pass through theconductor. In some cases, the controller can cause the conductor toexhibit a variable resistance.

The sensor can be a pressure sensor. As shown in FIG. 3, the sensor canbe connected to the hydrogen gas conduit 314 between hydrogen generator112 and hydrogen fuel cell 114. Thus, the sensor can sense pressure dueto hydrogen gas accumulation. If the pressure is high, then the sensorcan send a signal to the controller to reduce hydrogen gas production.If the pressure is low, then the sensor can send a signal to thecontroller to increase hydrogen gas production.

The sensor can be a voltage sensor. In such cases, the sensor can sensethe voltage being produced by the hydrogen fuel cell. If the voltage istoo low, then the voltage sensor can send a signal to the controller toincrease hydrogen gas production (and thereby increase voltage producedby the fuel cell). On the other hand, if the voltage is too high, thenthe voltage sensor can send a signal to the controller to decreasehydrogen gas production.

Other embodiments are within the scope of the following claims.

1. An electrochemical hydrogen generator comprising: a housing includinga hydrogen outlet; an anode in the housing including an oxidizablematerial; a cathode in the housing including a hydrogen generationcatalyst; and an ionically conductive, electrically insulative separatorlayer between the anode and the cathode.
 2. The hydrogen generator ofclaim 1, further comprising an aqueous ionic electrolyte within thehousing.
 3. The hydrogen generator of claim 1, wherein the oxidizablematerial comprises a metal.
 4. The hydrogen generator of claim 3,wherein the oxidizable material comprises a metal selected from thegroup consisting of a Group Ia metal, a Group Ib metal, a Group IIIametal, a Group IIb metal, iron, tin, manganese, titanium, zirconium andcombinations thereof.
 5. The hydrogen generator of claim 1, wherein theseparator comprises a non-woven fibrous polymer fabric.
 6. The hydrogengenerator of claim 5, wherein the non-woven fibrous polymer fabric islaminated to cellophane.
 7. The hydrogen generator of claim 6, whereinthe non-woven fibrous polymer fabric comprises polyvinyl alcohol fibers.8. The hydrogen generator of claim 1, wherein the cathode furthercomprises a binder containing the catalyst.
 9. The hydrogen generator ofclaim 8, wherein the binder comprises a member selected from the groupconsisting of high density polyethylene and polytetrafluoroethylene. 10.The hydrogen generator of claim 1, wherein the hydrogen outlet includesa hydrophobic membrane arranged to prevent leakage of a liquid from thehousing.
 11. The hydrogen generator of claim 1, wherein the oxidizablematerial comprises a metal hydride selected from the group consisting oftitanium hydride, zirconium hydride, reversible hydrides of nickel orlanthanum, and misch metal alloys.
 12. The hydrogen generator of claim1, wherein the oxidizable material comprises a metal selected from thegroup consisting of zinc, aluminum, titanium, zirconium, and tin. 13.The hydrogen generator of claim 1, further comprising an alkalineelectrolyte disposed in the housing.
 14. The hydrogen generator of claim13, wherein the alkaline electrolyte comprises a member selected fromthe group consisting of aqueous sodium hydroxide and aqueous potassiumhydroxide.
 15. The hydrogen generator of claim 1, wherein the anode andthe cathode are connected by an electronic conductor, and the electronicconductor comprises a switch.
 16. The hydrogen generator of claim 15,wherein the hydrogen generates on its own power, when the switch isclosed.